Metathesis reactions using ruthenium or other transition metal complexes as catalysts are meanwhile well known and have been widely applied in organic synthesis (see e.g. WO 2004/035596, WO 2002/14376 or EP-A 1180108).
A metathesis catalyst of the formula
is described by Barbasiewicz et al in Organometallics, published on Web Jun. 17, 2006. The authors have shown that applying this catalyst in a ring closing metathesis reaction of N,N-diallyl-4-methylbenzenesulfonamide in dichloromethane at room temperature 41% of 1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrole was formed after a reaction time of 24 h. Upon reworking under the same conditions, the conversion was very poor (<3%) affording less than 1% of 1-(toluene-4-sulfonyl)-2,5-dihydro-1H-pyrrole and even at a higher reaction temperature (110° C. in toluene) the activity of this catalyst remained poor.
Object of the present invention therefore was to provide superior metathesis catalysts.
It was surprisingly found that a substitution in alpha position of the nitrogen atom significantly improved the activity of the catalysts.
It could be shown that the ruthenium complexes of formula I have the potential to be useful catalysts in metathesis reactions such as in the ring closing or cross metathesis reactions.